In recent times, the vortex shedding flow meter has been emerging as one of the most popular flow meters, as it employs no moving parts subjected to wear and tear, has a rugged and sturdy construction suitable for applications involving extreme temperatures and pressures, and provides a highly accurate and reliable flow measurement on the volume flow rate of all types of fluids. Indeed, the vortex shedding flow meter can be made to a truly ideal flow meter only if a couple of major short comings existing with the present-day vortex shedding flow meter can be rid of. The most serious weakness in the vortex shedding flow meters commercially available at the present time is its inability to measure flows of gaseous media at low velocities. As the most popular means for detecting the vortices shed by the vortex generator includes detection of the bending of a mechanical probe or deflection of a diaphragm or movement of a target under pressure fluctuation, etc., there arises an inevitable difficulty in detecting weak vortices carrying very low levels of momentum, which are associated with flows of low density fluid medium at low velocity.
Another weakness in the existing technology of the vortex shedding flow meters is the noise removal. Since the vortex sensors detect the mechanical reaction of the probe to the action of vortices, the transducers pick up all other mechanical actions effecting the probe, which include the structural vibrations of pipe lines transmitted to the probe, low frequency acoustical noises penetrating across the pipe wall, noises associated with flow fluctuations unrelated to the vortices, etc. The noise problem becomes particularly serious when the probe has to detect a low velocity flow of a low density fluid. Although the ultrasonic means for detecting the wake created by the vortex generator provides a solution to the aforementioned weakness in the present-day vortex shedding flow meters, the vortex shedding flow meter with ultrasonic wake detection has its own weakness of a quite different nature, which includes the error introduced by the bubbles and particles suspended in the fluid medium, lack of the ruggedness and durability and the temperature and/or pressure limitations in the applicability, etc.
The primary object of the present invention is to provide a vortex shedding flow meter capable of measuring flow velocities of very wide range from very low velocity to very high velocity.
Another object is to provide a vortex shedding flow meter of high sensitivity and high accuracy.
A further object is to provide a vortex shedding flow meter of highly rugged and durable construction, and dependable and consistent performance.
Yet another object is to provide a vortex shedding flow meter of wide range of applications including extreme temperatures and pressures.
Yet a further object is to provide a vortex shedding flow meter including a vortex generating member of stiff elongated structure with a blunt cross section and a vortex sensing member of slender elongated structure with substantially flat cross section oriented substantially parallel to the direction of the flow wherein the vortex generating member and the vortex sensing member are disposed substantially parallel to one another and substantially perpendicular to the direction of the flow.
Still another object is to provide a substantially discontinuous junction at least at one extremity of the vortex sensing member of the slender elongated structure wherein the slender vortex sensing member abruptly extends to a stocky extremity experiencing an abrupt change in the size and shape of cross section; whereby a small amount of lateral deflection of the slender vortex sensing member created by the vortices produces a high stress concentration at the junction of discontinuous cross section.
Still a further object is to provide a vortex shedding flow meter including means for sensing stress or strain occuring in a concentrated form at the junction of discontinuous cross section, which sensing means is installed adjacent to the junction of discontinuous cross section intermediate the substantially flat midsection and the stocky extremity of the vortex sensing member.
These and other objects of the present invention will become clear as the description thereof proceeds.